Trip pawl control mechanism



y ,1 I J. A. ENDERS TRIP PAWL CONTROL MECHANJIZSM Filed April 8, 1958 2 Shets-Sheet'l i 8 .0 E Q H8- Q a. FI v I ,6 w Q .k 3 1 w A: Q w g m 1 om 1 w v k &

INVENTOR JOHN A. ENDERS TTdRNEYS July 28, 1959 J. A. ENDERS TRIP PAWL CONTROL MECHANISM Filed April 8, 1958 2 Sheets-Sheet 2 INVENTOR I)? A. ENDERS ATTORNEYS f United States Patent O TRIP PAWL CONTROL MECHANISM John A. Enders, Simsbury, Conn., assignor to Royal McBee Corporation, Port Chester, N.Y., a corporation of New York Application April 8, 1958, Serial No. 727,099

Claims. (Cl. 197-'17) This invention relates to a trip pawl control mechanism and more particularly relates to a machanism for controlling the latched and unlatched condition of the trip pawls of an electric twpewriter. More specifically the invention relates to a means for insuringthat when any of the trip pawls of an electric typewriter are unlatched, these pawls cannot reassume their respective latched lCOlldllIlOlJS unless each such pawl and its related linkage has been properly actuated by the power roll of the typewriter.

In conventional type actions wherein a trip pawl is released for movement into engagement with a power roll there is no provision for accommodating the operational situation wherein said trip pawl fails to drop into proper engagement with the power roll and is thrown back into the latched condition without partaking of its normal power driven stroke. When a key operated linkage of a typewriter is actuated and the related trip pawl fails to properly engage the power roll as above described, the typewriter will drop a character, i.e. there will be no actuation of the particular type bar in response to the operation of its associated key operated linkage. This type of malfunction of a trip pawl rarely occurs in the operation of electric typewriters and may be easily remedied by a typist by simply redepressing the key associated with said trip pawl. However, when the typewriter involved is being automatically operated by and in conjunction with perforated tape readers or other similar types of data processing apparatus, the above noted malfunction of a trip pawl is usually not correctable during a typing operation. Here there is no way to get a repeat signal from a record reader for reactuating the key linkage associated with a previously released trip pawl which has failed to properly engage the typewriter power roll. When letters or any other characters are so dropped the typed material will contain either mis-spelled words, incorrect punctuation, Wrong numbers, or combinations of these defects. Obviously such errors are undesirable and the instant invention is directed toward overcoming the possible occurrence of these difi'lculties.

One object of the invention is to provide an improved control mechanism for each of the trip pawls used in conjunction with a power driven roll.

Another object of the invention is to provide an improved means for preventing the -dropping of characters during the operation of an electric typewriter.

Another object of the invention is to .provide an improved control mechanism for the trip pawls of an electric typewriter whereby each pawl, after being released from its latched condition, cannot reassume said latched condition until after it has properly engaged and been actuated by the power roll of the typewriter.

Another object of the invention is to provide a bistable latching mechanism for each of the trip pawls of an electric typewriter whereby any released trip pawl cannot be restored to operative engagement with its ass0- ciated latch until a power stroke of said pawl has been efiected.

2,896,765 Patented July 28, 1959 Other objects of the invention will become apparent as the disclosure progresses.

In the drawings:

Fig. 1 is a side elevational view in partial section and shows the normal conditions of the various parts comprising one type action of the instant typewriter.

'Fig. 2 is a detailed side view of the. instant trip pawl control mechanism.

Fig. 3 is a side elevational view showing a few of the parts of Fig. 1 in their respective active positions, and,

Fig. 4 is a side elevational view showing the parts of Fig. 3 being restored to their respective normal positions.

Unless otherwise specified it will be understood that the various components of the apparatus shown in the instant drawings are suitably supported by the side frames of the machine.

On the main frame 5, Fig. 1, of the instant typewriter there is mounted a movable carriage 6 which rotatably supports a cylindrical platen 7. A pivotally mounted type bar 8 is supported in the segment 9 of the instant machine and is adapted to be arcuately moved into printing engagement with a record sheet positioned in said carriage 6. In that all the type actions for the instant typewriter are similar a detailed consideration of one thereof will suffice here. Referring to Fig. 1 each of said type actions is generally comprised of four major components, to wit; a key operated linkage 10, a type bar actuating linkage 12 including a trip pawl 14 and ,a trip pawl control mechanism 16. In that the first three of these components are conventional in nature only a brief description of the construction and operation thereof need to be made here. The key operated linkage 10 comprises a bell crank 20 which is pivotally mounted on the transverse shaft 21. Pivotally mounted on the outer end of the rearwardly extending bell crank arm 22 is a detent 25 which is rotatably biased in a clockwise direction by means of spring 26. The clockwise limit of movement of cam detent '25 is determined by the engagement of the upper edge of the detent projection '27 with the bent-off car 28 formed on said bell crank arm 22. The lower edge of detent 25 is formed so as to provide an inclined Icamming surface 29. v

-The linkage 10 may be operated by depressing the key 34 secured to the key lever 35 which is pivotally mounted upon the transverse member '36 of the typewriter frame. In that the upper end 37 of said key lever engages the rearward edge of the depending bell crank arm 38, said key depression will cause a clockwise displacement of bell crank 20 against the action of the spring 39 which is operatively connected between said key lever 35 and said bell crank 20.

The type bar operating linkage 12 comprises a sub lever 40 which is pivotally mounted on the transverse member 41 of the typewriter frame and which is articu lately connected to the lower end of the said type bar 8 by means of a link 42. Pivotally connected to the sub lever 40 is an action plate 43, the upper and lower projections 44 and 45 formed at the forward end of said plate 43 being respectively slidably disposed in the slots 46 and 47 of the comb member 48 secured to said frame member 36. The forward end of the action plate 43 is biased upwardly by the tension spring 50, the upper limit of movement of plate 43 here being determined by the sliding engagement of the plate bent-ofi ear 55 with the lower surfaces of the upper arm 46 or said comb member 48. The trip pawl 14 is pivotally mounted on plate 43 and is rotatably biased in a clockwise direction by means of the spring 92. The forwardly extending portion 62 of said trip pawl is provided with an inclined camming edge 63, Fig. 3, which is adapted to cooperate with the rearmost edge 64 of a bracket 65 which is fixedly supported by said frame member 36. The rearward end of the trip pawl is provided with a depending tooth 66, Fig. 1, which is adapted to be lowered into operative engagement with the teeth 67 of the said power roll 15. The serrated roll 15 is rotatably mounted in the side frames of the machine and is rotatably driven in a counterclockwise direction 70 by any suitable motor means. i l

' When the'trip pawl '14 is permitted to drop into operative engagement with the teeth of the power roll 15 by the depression of key 34 the action plate 43 will be driven forwardly in the usualmanner thereby effecting a printing stroke of the type bar 8. Near the end of the forward stroke of the action plate 43, the said camming edge 63 of the trip pawl 14 will engage said bracket edge 64 thereby causing pawl 14 to be displaced in a counterclockwise direction toward its normal position. This action is conventional in nature and need not be further panicularized here. I

The structural aspects of the trip pawl control mech-' anism 16 will be explained with reference to Fig. 2. Said mechanism comprises a trip pawl latch 75 which is mounted for rotational and translational movements by means of the headed action plate stud 76 which slidably engages the walls of an elongated slot 77 formed in the said latch. A bent-off ear 78 is formed on the lower forward edge of said latch. The latch 75 is provided at its rearward end with a shoulder hook 80 having a bent-off ear 81 that is adapted to normally engage the notch 82 formed in rearward end of said trip pawl 14. Latch 75 is rotatably biased in a clockwise direction by a spring 83 which is anchored to said action plate 43, the clockwise limit of movement of latch 75 being determined by engagement of said latch ear 78 with the lower edge of the action plate 43. The action of spring 83 serves also to translatably bias said latch so that therearward end of said slot 77 is normally engaged with the said stud 76. The forward end of latch 75 is provided with a bent-off car 85 which is disposed in the aperture 86 formed in the plate 43. A latch actuator 90, pivotally mounted on the action plate stud 91, is rotatably biased in a counterclockwise direction by means of a spring 92 which is operatively disposed between said actuator and the trip pawl 14. The rearward end of actuator 90 is formed with a bent-01f car 95, which is disposed beneath the said detent 25, and with a notch 96, while the forward end thereof is provided with a projection 97. Said projection 97 is adapted to cooperate with the rearmost edge 98 of a bracket 100 that is fixedly secured to the said bracket 65.

Figs. 1 and 2 show the normal relative positions for the respective parts of the instant type action. In the normal position of the latch 75 the ear 81 thereof lies in the path of motion of the rearward end of the trip pawl 14 and thereby holds the latter from being spring urged into operative engagement with the power roll 15. The latch actuator 90 is normally spring urged to its counterclockwise position wherein the notch 96 thereof overlies the ear 85 of latch 75. When the said linkage is operated 'by the manual depression of the key 34 or by the operation of any suitable power means, the lower edge 29 of the camming detent 25 will engage the bent-off car 95 of the latch actuator 90 and will rotate the latter in a clockwise direction against the action of spring 92. This will cause the latch 75 to rotate in a counterclockwise direction against the action of its spring 83 to the release position shown in Fig. 3 wherein the trip pawl 14 is free to swing into operative engagement with the teeth of power roll in a counterclockwise direction, however the latch 75 accommodates this movement by being displaced clockwise through an are having a center of curvature at or near the latch spring anchor hole 79, Fig. 3. This arcuate translatory displacement of latch 75 occurs generally upwardly and to the right, as seen in Fig. 3, until said latch ear 78 engages the lower edge of the action plate 43. In that the mutually engaged notch 96 and ear 85 are now just below the line of centers of the two pivot studs 76 and 91 a yieldably wedging action will result whereby latch 75 is prevented from translating rearwardly against the action of its spring '83, and whereby the actuator 90 is prevented from rotating in a counter clockwise direction under the action of its spring 92. Under these condi- 15; When the latch 75 reaches its release or countertions the latch 75 remains in its release position of Fig. 3 so that if, for any reason, there is a counterclockwise rebound of the trip pawl 14 after unsuccessfully engaging the power roll 15, the trip pawl will not reengage the latch 75, as in Fig. 1, but will be free to again drop into engagement with said power roll 15.

When the trip pawl 14 has properly engaged the power roll as shown in Fig. 3 the action plate 43 and remaining portions of the type bar actuating linkage 12 will be power driven forwardly in the usual manner to thereby operatively actuate the associated type bar 8. Near the end of this forward stroke of plate 43 the projection 97 of the actuator 90 will engage the rearward edge 98 of said fixed bracket 100. In so doing the actuator 90 will be forcibly rotated in a counterclockwise direction as illustrated by Fig. 4. Here the yieldably wedging action between the actuator 90 and latch 75 will be overcome by reason of latch 75 being forcibly translated rearwardly against the action of spring 83 so that the right end of the latch slot 77 moves farther away from the said pivot stud 76. Once the actuator notch 96 is thus able to move clear from the bent off ear of the latch 75, actuator will be restored to its normal counterclockwise position by spring 92 and latch 75 will be restored to its normal trip pawl retaining position as shown in Fig. 4.

The restoration of latch 75 to its normal position occurs just prior to the time that the trip pawl 14 is cammed upwardly out of engagement with the power roll 15 by the cooperate relative movement between the forwardly disposed trip pawl camming edge 63 and the edge 64 of said bracket 65. When this induced counter clockwise movement of the trip pawl is completed ,as illustrated in Fig. 4, the ear 81 of latch 75 will again engage the trip pawl notch 82 thereby retaining said trip pawl 14 in its normal Fig. 1 position.

From the above described operation it will be apparent that the latch 75 is bistable, i.e. it may be moved to and held in either of two stable positions, to wit; the trip pawl retaining position of Fig. l and the release position of Fig. 3. Further when any trip pawl is released the associated latch will not be able to reengage said trip pawl until the latter, and its action plate, have partaken of their normal power stroke. In this way when any typewriter key is depressed the associated type bar will always be actuated with no possibility of the released trip pawl ever being relatched after improperly rebound ing away from the power roll.

It will be apparent that the above described trip pawl control mechanism may be utilized in various types of power operated devices, such as tape punches, wherein a plurality of movable elements are to be selectively coupled to a driven power roll. Also the instant invention may be used to control the operation of the roll cam supporting arms of typewriters having friction type power rolls.

While there is in this application specifically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration only and that the invention may 'be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

The invention claimed is:

1. In a type action for a typewriter, a type bar operating linkage, a key operated linkage, a driven power roll,

and means controlled by said key operated linkage for operatively coupling said type bar operating linkage to said power roll; said means comprising, a trip pawl connected to said type bar linkage and being movable into and out of operative engagement with said power roll, latch means mounted on said type bar operating linkage for normally releasably retaining said pawl out of engagement with said power roll, said latch means being movable to normal and release positions, and means con trolled by said key operated linkage for moving said latch means to said release position wherein said trip pawl is free to move into operative engagement with said power roll, said last mentioned means including a means for retaining said latch means in said release position until said type bar operating linkage partakes of its operative stroke. 2. In a type action for a typewriter, an action plate, a trip pawl movably mounted on said plate, a trip pawl latch movably mounted on said plate and being adapted to be moved to two stable positions relative to said plate, said latch being supported for translational and rotational movement and being adapted to normally operatively engage said trip pawl, and a trip pawl latch actuator movably mounted on said plate and adapted to engage and determine at least one of the two stable positions of the said trip pawl latch.

3. In .a type action for a typewriter, an action plate, a spring biased trip pawl movably mounted on said plate, a trip pawl latch mounted on said plate and adapted to be moved to two stable positions, said latch when in said positions respectively preventing and permitting the spring biased operative movement of the said trip pawl, and a latch retaining means movably mounted on said plate for releasably retaining said latch in at least one said positions.

4. In a type action for a typewriter, an action plate, a spring biased pawl rotatably mounted on said plate, a spring biased trip pawl latch mounted no said plate for rotational and translational movement to a normal pawl engaging position and to a stable pawl release position, and a spring biased latch actuator pivotally mounted on said plate and cooperating with said latch to retain the latter in at least one of said positions.

5. In a typewriter having a type bar operating linkage, a key operated linkage, and a power roll; the improvement comprising, a trip pawl movably mounted on said type bar operating linkage and movable into operative engagement with said power roll, latch means mounted on said type bar operating linkage and being movable to a trip pawl release position and to a trip pawl retaining position, bias means on said type bar operating linkage for normally maintaining said latch means in said trip pawl retaining position, actuator means mounted on said type bar operating linkage and operated in response to the actuation of said key operated linkage for moving said latch means to said trip pawl release position, and means on said actuator means operative in response to the operation of said type bar operating linkage for permitting said latch means to return to its said trip pawl retaining position.

References Cited in the file of this patent UNITED STATES PATENTS 

